The present invention is directed to an improved screening apparatus. More specifically, the present invention is directed to a bowl-shaped static screen having improved annular distribution of influent thereto and a system assuring solids removal from the screen.
A variety of inclined, static screens have been used for the separation of solids-containing liquids. One such screen system is disclosed in U.S. Pat. Nos. 2,872,041, and 2,916,142. Similar screening systems employing a conical arrangement have also been used; see U.S. Pat. No. Des. 226,398. The latter, conical or bowl-shaped arrangement is believed to be more efficient from a space-saving standpoint and is less subject to damage because of its inherently closed nature. Another advantage of the bowl-shaped static screen is the inherent decrease in the width of the screen toward the outlet. The highest rate of flow is experienced at the upper or influent end of the screen. As the influent moves downwardly along the screen, the flow is greatly reduced as liquid passes through the screen to the effluent receiver. As the flow decreases, less screen width is necessary. It is further believed that in some instances, this natural reduction in width of the screen may be advantageous to the promotion of continued flow in the lower portion of the screen.
For both straight and bowl-shaped static screens, controlled distribution of influent is advantageous to assure maximum utilization of the screen area. It is also of benefit for maximum screen efficiency, screen life and uniformity of separation that distribution of influent be as uniform as possible to all portions of the screen. Furthermore, varying flow rates and influent properties require variations in the distributor geometry to gain maximum efficiency. These requirements have been more easily solved through the use of screens having straight, rather than curved, horizontal elements. Screens having straight horizontal elements employ straight inlet orifices which are more easily balanced and adjusted to obtain proper and uniform flow to the screen.
Another difficulty encountered with static screens is the collection of solids near the outlet thereof. It has been common practice to allow the solids collecting at the lower end of the screen to build up until the material naturally moves to the concentrate receiver. In some instances, this build-up may result in a loss of separating efficiency. Of course, hand scraping of a screen is possible; however, such practice is generally objectionable because of the labor involved and the dependence on timely attention thereto.